Update nightly CI pipelines to 6.1 instead of 6.0 #1243

Job	Run time
Construct integration test matrix	3s
Vsock tests	1m 53s
Benchmarks / Construct Benchmarks matrix	5s
Cxx interop / Construct Cxx interop matrix	4s
Unit tests / Construct unit test matrix	4s
Soundness / API breakage check	1m 59s
Soundness / Documentation check	1m 58s
Soundness / License headers check	8s
Soundness / Broken symlinks check	2s
Soundness / Format check	48s
Soundness / Python lint check	5s
Soundness / Shell check	39s
Soundness / Unacceptable language check	2s
Soundness / YAML lint check	5s
Integration tests / Linux (5.9)	22m 52s
Integration tests / Linux (5.10)	21m 16s
Integration tests / Linux (6.0)	23m 40s
Integration tests / Linux (nightly-6.0)	23m 48s
Integration tests / Linux (nightly-main)	23m 11s
Benchmarks / Benchmarks / Linux (5.9)	5m 19s
Benchmarks / Benchmarks / Linux (5.10)	4m 57s
Benchmarks / Benchmarks / Linux (6.0)	5m 16s
Benchmarks / Benchmarks / Linux (nightly-6.0)	6m 23s
Benchmarks / Benchmarks / Linux (nightly-main)	4m 10s
Unit tests / Unit tests / Linux (5.9)	3m 48s
Unit tests / Unit tests / Linux (5.10)	3m 44s
Cxx interop / Cxx interop / Linux (5.9)	1m 8s
Unit tests / Unit tests / Linux (6.0)	4m 13s
Cxx interop / Cxx interop / Linux (5.10)	1m 6s
Unit tests / Unit tests / Linux (nightly-6.0)	4m 35s
Cxx interop / Cxx interop / Linux (6.0)	1m 16s
Unit tests / Unit tests / Linux (nightly-main)	4m 32s
Cxx interop / Cxx interop / Linux (nightly-6.0)	1m 31s
Cxx interop / Cxx interop / Linux (nightly-main)	1m 30s
	2h 56m 10s

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